Browsing by Issue Date, starting with "2004-02-03"

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Control system for an electrostatically-driven microelectromechanical device
(2004-02-03)
Chiou
;
Jin-Chern
;
Lin
;
Yu-Chen
The present invention relates to a control system for an electrostatically-driven microelectromechanical device, which uses multiple electrodes to control the microelectromechanical device, i.e. the lower driven electrode of a capacitor with known two parallel driven electrodes is cut into a number of small electrodes. By selecting an electrode pattern for a desired electrostatic force, it is capable of altering the non-linearity of the device based on various applications and achieving a characteristic such as a linear driven, digital driven, or ultimately optimal driven manners, which is able to reach high operation accuracy for the existing circuit that only possesses a limited accuracy.
Method for transferring epitaxy layer
(2004-02-03)
Wu
;
YewChung Sermon
;
Lin
;
PeiYan
A method for transferring an epitaxy layer is provided. The method includes steps of (a) providing a first substrate, (b) forming a first epitaxy layer on the first substrate, (c) forming a masking layer having at least a pattern on the first epitaxy layer, (d) forming a second epitaxy layer on the masking layer, (e) bonding a second substrate to the second epitaxy layer, and (f) removing the masking layer and separating the second epitaxy layer from the first epitaxy layer, thereby the second epitaxy layer being transferred to the second substrate.
A positive charge at position 33 of thioredoxin primarily affects its interaction with other proteins but not redox potential
(2004-02-03)
Lin, TY
;
Chen, TS
;
生物科技學系
;
Department of Biological Science and Technology
Oxidoreductases of the thioredoxin superfamily possess the C-X-X-C motif. The redox potentials vary over a wide range for these proteins. A crucial determinant of the redox potential has been attributed to the variation of the X-X dipeptide. Here, we substitute Lys for Gly at the first X of Escherichia coli thioredoxin to investigate how a positive charge would affect the redox potential. The substitution does not affect the protein's redox potential. The equilibrium constant obtained from pairwise reaction between the mutant and wild-type proteins equals 1.1, indicating that the replacement does not significantly affect the thiol-disulfide redox equilibrium. However, the catalytic efficiency of thioredoxin reductase on the G33K mutant decreases approximately 2.8 times compared to that of the wild type. The mutation mainly affects K-m, with little effect on k(cat). The mutation also inhibits thioredoxin's ability to reduce insulin disulfide by approximately one-half. Whether the mutant protein supports the growth of phages T3/7 and f1 was tested. The efficiency of plating (EOP) of T3/7 on the mutant strain decreases 5 times at 37 degreesC and 3 x 10(4) times at 42 degreesC relative to that of the wild-type strain, suggesting that interaction between phage gene 5 protein and thioredoxin is hindered. The mutation also reduces the EOP of phage f1 by 8-fold at 37 degreesC and 1.5-fold at 42 degreesC. The global structure of the mutant protein does not change when studied by CD and fluorescence spectra. Therefore, G33K does not significantly affect the overall structure or redox potential of thioredoxin, but primarily interferes with its interaction with other proteins. Together with the G33D mutation, the overall results show that a charged residue at the first X has a greater influence on the molecular interaction of the protein than the redox potential.
Thixocasting of hypereutectic Al-25Si-2.5Cu-1Mg-0.5Mn alloys using densified powder compacts
(2004-02-05)
Chen, CM
;
Yang, CC
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Hypereutectic Al-Si alloys with fine and evenly distributed Si grains have superior mechanical characteristics and are usually fabricated by powder metallurgy (PM). However, PM methods cannot easily achieve the net-shape forming of complicated engineering parts. This work presents a novel method, which combines consolidating prealloyed powders with thixocasting the consolidated compacts, for net-shape forming of a hypereutectic Al-25Si-2.5Cu-1Mg-0.5Mn alloy. Experimental results indicate that as-thixocast specimens fabricated with larger powders and greater deformations have higher tensile strengths. Fractographs show that the strengths were strongly affected by the detrimental oxides that originated in the powder compacts, and that the oxides could be effectively eliminated by plastic deformation during thixocasting. Isothermal heat-treatment tests of the powders revealed two distinct ranges of Si grain-coarsening rates in the semi-solid temperature range. The Si grains ripened slowly at temperatures from 540 to 560degreesC, considered as the appropriate processing temperature range for obtaining fine Si grain. This low coarsening rate was explained by the diffusion of Si through the semi-solid matrix that only consists of a little liquid, since Si diffuses in solid Al much more slowly then in liquid Al. (C) 2003 Elsevier B.V. All rights reserved.
Edge instability elimination of GaAs/ALGaAs MQW avalanche transit time oscillators by P(+) substrate
(2004-02-05)
Meng, CC
;
電信工程研究所
;
Institute of Communications Engineering
The p(+) substrate plays an important role on the edge stability of p(+)n multiquantum well avalanche transit time devices. The p(+)n multiquantum well avalanche transit time devices on n(+) substrate easily burn out along the device edge at low breakdown current. The same structure on p(+) substrate can have the desired band diagram on device edge to eliminate edge burn-out and CW operation is thus achieved at 100.3 GHz. (C) 2004 Wiley Periodicals, Inc.
Adsorption and decomposition studies of t-butylamine, diethylamine, and methylethylamine on Si(100)-(2 x 1)
(2004-02-05)
Wu, JB
;
Yang, YW
;
Lin, YF
;
Chiu, HT
;
應用化學系
We have studied chemisorption and thermal decomposition of tert-butylamine (TBA), diethylamine (DEA), and methylethylamine (MEA) on Si(100)-(2 x 1) with synchrotron-based X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Adsorption at cryogenic temperature leads to molecularly intact chemisorption (dative-bonding via the nitrogen lone pair) and dissociative chemisorption via N-H scission, producing distinct N 1s peaks at binding energies of 401.1 and 398.2 eV, respectively. The corresponding change for C 1s core level is also significant, and a 0.9 eV shift toward lower binding energy is found for DEA, suggesting a high degree of charge redistribution between two adsorption configurations. Upon warming to room temperature, the adsorbed amines almost completely transform into dissociative chemisorbed forms. Thermal decomposition of TBA at elevated temperatures produces desorption species of isobutylene via gamma-H elimination, hydrogen cyanide, and H-2. In comparison, DEA and MEA decompose thermally to desorb imine via P-H elimination, ethylene via beta-H elimination, hydrogen cyanide, and H2. Eventually, silicon nitride and silicon carbide are formed. Distinct decomposition pathways lead to a C/N ratio variation among the products, with TBA yielding the lowest C/N ratio.
Comment on "Triplet-to-singlet exciton formation in poly(p-phenylene-vinylene) light-emitting diodes" - Reply
(2004-02-06)
Lin, LC
;
Meng, HF
;
Shy, JT
;
Horng, SF
;
Yu, LS
A new trans-to-cis photoisomerization mechanism of azobenzene on the S-1(n,pi*) surface
(2004-02-12)
Diau, EWG
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
;
Institute of Molecular science
The rotation-inversion controversy for the photoisomerization mechanism of azobenzene has been addressed on the basis of the CASSCF calculations for the excited-state relaxed surface scan along the CNN bending (inversion), the CNNC torsion (rotation), and the concerted CNN bending (concerted inversion) reaction pathways. According to our calculated results, the inversion channel involves a substantial energy barrier and a large S-0-S-1 energy gap so that it is a highly unfavorable channel to be considered for an efficient electronic relaxation. The rotation channel is essentially barrierless with a conical intersection close to the midpoint of the pathway to reasonably account for the subpicoseond to picosecond relaxation times observed in recent ultrafast experiments. Along the concerted inversion reaction path, a sloped conical intersection (S-0/S-1 CI_inv) was found to have the geometry close to a linear CNNC configuration. When the photoexcitation occurs in the S-2 state, the concerted inversion channel may be open and the S-0/S-1 CI_inv would become energetically accessible to produce more trans-S-0 isomers. A new mechanism is proposed to rationalize the early experimental results for the following two cases: (1) the trans-to-cis photoisomerization quantum yields on S-2 excitation are much lower than the yields on S-1 excitation; (2) the yields from both the S-2 and the S-1 excitations become essentially equal when the rotation channel is blocked by chemical modification or in an inclusion complex.
Electrical and dielectric behavior of fluorite-like Sr0.8Bi2.6Ta2O9 thin films pyrolyzed and thermally annealed at 450 degrees C
(2004-02-15)
Huang, CH
;
Chou, HY
;
Lian, CW
;
Tseng, TY
;
電子工程學系及電子研究所
In this paper, we present the results of the fabrication and characterization of fluorite-like Sr0.8Bi2.6Ta2O9 (SBT) thin films spin-coated on Ir (50 nm)/SiO2 (100 nm)/p-type (100)Si substrates using the metal-organic decomposition (MOD) technique. The SBT films prepared at 450 degreesC under various annealing times were characterized by X-ray diffraction (XRD) as fluorite phase. The polarization versus electric field (P-E) behavior of SBT thin films pyrolyzed and annealed at 450degreesC for 60 min was linear with dielectric constant of 100. The 450 degreesC annealed films have the leakage current density of about 4 x 10(-8) A/cm(2) at 200 kV/cm. The dependence of cumulative failure on dielectric breakdown field and time-dependent dielectric breakdown studies for these paraelectric SBT films indicated that the longer the annealing time, the better the breakdown field, whereas the film with no annealing treatment had a lifetime of over 10 years on operation at the electric field of 0.8 MV/cm. (C) 2003 Elsevier B.V. All rights reserved.
MOCVD growth of AlN/GaN DBR structures under various ambient conditions
(2004-02-15)
Yao, HH
;
Lin, CF
;
Kuo, HC
;
Wang, SC
;
光電工程學系
The high-reflectivity AlN/GaN distributed Bragg reflector (DBR) structures were realized by metal organic chemical vapor deposition (MOCVD) growth under pure N-2 ambient for AlN epilayer growth. The highest peak reflectivity of about 94.5% with a stopband width of 18 nm at a center wavelength of 442 nm was obtained. For the DBR structure with AIN layer grown under mixture of N-2/H-2 and pure H-2 conditions, the center wavelength was blue-shifted to 418 and 371 nm and the peak reflectivity also showed a reduction to 92% and 79%, respectively. The stopband width also decreases with increasing H-2 contents. The surface roughness and the grain size of the grown DBR structures showed an increase with increasing the H-2 ambient gas ratio. For realization of a high reflectivity and broad bandwidth of AlN/ GaN DBR by using the MOCVD growth method, the pure N-2d ambient gas for growth of AIN layer should be preferable and optimal condition. (C) 2003 Elsevier B.V. All rights reserved.
Self-rated health among young people with type 1 diabetes in relation to risk factors in a longitudinal study
(2004-02-15)
Huang, GH
;
Palta, M
;
Allen, C
;
LeCaire, T
;
D'Alessio, D
Care for type 1 diabetes mellitus should both alleviate the physical complications of the disease and improve overall quality of life. The Wisconsin Diabetes Registry, comprising a population-based cohort that is followed longitudinally from diagnosis of type 1 diabetes, provided the authors with a unique opportunity to examine quality of life in children, adolescents, and young adults with type 1 diabetes and its relation to both sociodemographic and clinical risk factors. The authors analyzed data from 1987-2002 with a mean of 10.2 years' duration of diabetes (n = 569). They used ordinal-scaled self-rated global health as a measure of quality of life. In this paper, they propose a random-effects model for drawing inferences on individuals regarding the relation of longitudinally measured quality of life to multiple risk factors. Results showed that male gender, higher parental socioeconomic level, younger age at diabetes diagnosis, shorter diabetes duration, no hospitalization in the preceding 6 months, lower glycosylated hemoglobin level, and questionnaire responses by a person other than the subject were independently associated with better reported health. The authors found that individuals varied in their reported health even after adjustment for all identified risk factors. This could imply either that there is variability in perception even with the same health status or that there are independent unmeasured risk factors for poor health in persons with type 1 diabetes.
Controlled placement of self-organized Ge dots on patterned Si (001) surfaces
(2004-02-15)
Lee, HM
;
Yang, TH
;
Luo, GL
;
Chang, EY
;
材料科學與工程學系
The positioning and ordering of the self-organized Ge dots were controlled using the ultra high-vacuum chemical molecular epitaxial growth of Ge on electron beam lithographically patterned Si (001) substrates. The experimental results indicate that the edge smoothness of the etched Si holes affects the distribution and long-range ordering of the Ge dots formed. With optimized etching conditions, the Ge dots can be grown uniformly on the edges of the holes etched on the patterned Si substrates. The sizes of the Ge dots are approximately 10 nm. The proposed, technique can be applied to the fabrication of regimented arrays in signal processing applications.
Spatially-resolved photoluminescence studies of V-shaped pits on Al0.16Ga0.84N
(2004-02-15)
Huang, HY
;
Ku, CS
;
Ke, WC
;
Tang, NE
;
Peng, JM
We have studied optical properties of V-shaped pits on Al0.16Ga0.84N. The microphotoluminescence spectrum from the pit center shows a broader and stronger emission at 350 nm than the near-band-edge emission at 336 nm from nonpit regions. The results indicated specific defect levels associated with the V-shaped pits. Furthermore, after using atomic force microscopy to probe the surface electrical potential with a conductive tip, the pit's potential was similar to0.2 V lower than its surrounding region. A simplified energy diagram is tentatively proposed to interpret our observation. (C) 2004 American Institute of Physics.
Ultra-high-density InGaN quantum dots grown by metalorganic chemical vapor deposition
(2004-02-15)
Tu, RC
;
Tun, CJ
;
Chuo, CC
;
Lee, BC
;
Tsai, CE
This study examined how the duration of SiNx treatment on an underlying GaN layer affects the optical property, surface morphology and density of following InGaN quantum dots (QDs). InGaN QDs with extremely high density of near 3 x 10(11) cm(-2) exhibited strong photoluminescence (PL) emission at room temperature (RT). Increasing the duration of the SiN, treatment of the underlying GaN layer, the RT-PL peak of the following InGaN nano-islands and QDs was found to be red-shifted from the violet to the greenish region, and the spectrum was broadened. Additionally, the average height of InGaN nano-islands and QDs increased with the duration of SiNs treatment, explaining the redshift of the RT-PL peak.
High nitrogen content InGaAsN/GaAs single quantum well for 1.55 mu m applications grown by molecular beam epitaxy
(2004-02-15)
Wang, JS
;
Kovsh, AR
;
Hsiao, RS
;
Chen, LP
;
Chen, JF
The growth of high nitrogen content InGaAsN/GaAs single quantum well (SQW) for 1.55 mum applications on GaAs substrates using solid source molecular beam epitaxy and radio frequency plasma nitrogen source is reported. The nitrogen composition was determined using an X-ray diffractometer combined with dynamic simulation. The crystal and optical qualities of highly strained InGaAs/GaAs SQW grown at low temperature can be significantly improved by nitrogen incorporation due to reducing the lattice mismatch. Without the formation of additional nonradiative recombination in InGaAsN SQW with nitrogen composition up to 4.1% which corresponds to wavelength of 1.46 mum was achieved. The longest room-temperature PL peak wavelength obtained in this study is 1.59 mum by increasing the nitrogen composition up to 5.3%. And, the photoluminescence intensity of high nitrogen content InGaAsN SQW can be improved significantly by decreasing the growth temperature due to suppression of the phase separation of InGaAsN alloy. Our results show the potential for the fabrication of 1.55 mum InGaAsN QW lasers on GaAs substrates. (C) 2003 Elsevier B.V. All rights reserved.
Complex fiber grating structures fabricated by sequential writing with polarization control
(2004-02-15)
Chu, KP
;
Lai, YC
;
Sheu, LG
;
光電工程學系
;
Department of Photonics
We propose a flexible method for fabricating complex fiber grating structures based on sequential writing for fiber gratings with polarization control of the UV source beam. Pure apodized as well as arbitrary phase-shifted fiber Bragg gratings (FBGs) can be fabricated in a single scan. Experimental examples of raised-cos(2) apodized and dispersionless FBG filters are given to demonstrate the feasibility of this method. (C) 2004 Optical Society of America.
史記
(2004-02-15)
管管
Characterization of poly(vinyl pyrrolidone-co-isobutylstyryl polyhedral oligomeric silsesquioxane) nanocomposites
(2004-02-15)
Xu, HY
;
Kuo, SW
;
Huang, CF
;
Chang, FC
;
應用化學系
Poly(vinyl pyrrolidone-co-isobutyl styryl polyhedral oligomeric silsesquioxane)s (PVP-POSS) were synthesized by one-step polymerization and characterized 13 using FTIR, high-resolution H-1-NMR, solid-state C-13-NMR, Si-29-NMR, GPC, and DSC. The POSS content can be controlled by varying the POSS feed ratio. The T-g of the PVP-FOSS hybrid is influenced by three main factors: (1) a diluent role of the POSS in reducing the self-association of the PVP; (2) a strong interaction between the POSS siloxane and the PVP carbonyl, and (3) physical aggregation of nanosized POSS. At a relatively low FOSS content, the role as diluent dominates, resulting in a decrease in T-g. At a relatively high POSS content, the last two factors dominate and result in T-g increase of the PVP-POSS hybrid. (C) 2003 Wiley Periodicals, Inc.
Spin-dependent Hall effect in semiconductor quantum wells
(2004-02-15)
Huang, HC
;
Voskoboynikov, O
;
Lee, CP
;
交大名義發表
;
National Chiao Tung University
We present a theoretical study of the spin-dependent scattering of electrons from screened attractive and repulsive impurities in III-V semiconductor quantum wells. The effective one-band Hamiltonian and the Rashba spin-orbit interaction are used. We demonstrated that the asymmetry of the spin-dependent skew-scattering and side-jump effect can lead to a quite large spin-dependent (anomalous) Hall effect at zero magnetic field in all-semiconductor quantum well structures. Our theory predicts a measurable spin-dependent Hall angle that reaches about 2.5x10(-3) rad for a CdTe/InSb/CdTe quantum well with impurities doped in the center of the well. (C) 2004 American Institute of Physics.
Experimental and quantum-chemical studies on photoionization and dissociative photoionization of CH2Br2
(2004-02-15)
Chiang, SY
;
Fang, YS
;
Sankaran, K
;
Lee, YP
;
應用化學系
The dissociative photoionization of CH2Br2 in a region similar to10-24 eV was investigated with photoionization mass spectroscopy using a synchrotron radiation source. An adiabatic ionization energy of 10.25 eV determined for CH2Br2 agrees satisfactorily with predictions of 10.26 and 10.25 eV with G2 and G3 methods, respectively. Observed major fragment ions CH2Br+, CHBr+, and CBr+ show appearance energies at 11.22, 12.59, and 15.42 eV, respectively; minor fragment ions CHBr2+, Br+, and CH2+ appear at 12.64, 15.31, and 16.80 eV, respectively. Energies for formation of observed fragment ions and their neutral counterparts upon ionization of CH2Br2 are computed with G2 and G3 methods. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. An upper limit of DeltaH(f,298)(0)(CHBr+)less than or equal to300.7+/-1.5 kcal mol(-1) is derived experimentally; the adiabatic ionization energy of CHBr is thus derived to be less than or equal to9.17+/-0.23 eV. Literature values for DeltaH(f,298)(0)(CBr+)=362.5 kcal mol(-1) and ionization energy of 10.43 eV for CBr are revised to be less than 332 kcal mol(-1) and 9.11 eV, respectively. Also based on a new experimental ionization energy, DeltaH(f,298)(0)(CH2Br2+) is revised to be 236.4+/-1.5 kcal mol(-1). (C) 2004 American Institute of Physics.